Enduring increase of the flexibility of the telecommunications network is one of industrial needs the satisfaction of which supports the demand of continually-rising levels of telecommunication traffic, with dynamic network optical systems leading the way as a solution that allows a light-path provisioning to distribute bandwidth of the traffic on an as-needed basis. Historically, systems required that a technician be involved to re-provision the optical light-paths of a network system, but more recent implementations are moving toward algorithm-controlled, remote sub-systems and reconfiguration time is becoming a new bottleneck of implementing such sub-systems.
Indeed, time spent reconfiguring an optical switch is time that the circuit is non-transmitting, which places stringent speed requirements on emerging optical switching technologies. The main benefits to using optical switches are that they these switches are protocol and bit-rate independent—the characteristics that alleviate the requirement for frequent upgrades in response to changing network fabrics and increasing data rates. Moreover, as the light-path redirection with the use of an optical switch is often effectuated in free space, a modular design of a system utilizing such switch can be scaled up, leading the way to the implementation of higher port count devices.
Currently existing versions of optical switches are subject to at least three main operational shortcomings, which (as recognized in the related art) limit the applicability of the existing devices. Among these drawbacks are the requirement of manual manipulation of a switch, a single point failure mechanism, and operation at a speed that falls short of meeting sub-millisecond application requirements. Optical switches based on an array of beam-redirecting devices have been discussed by the related art to address the above-identified shortcoming, however no solution offered to-date succeeded in a satisfactory fashion.
Three-dimensional (3D) microelectromechanical system (MEMS) devices, for example, employ two opposing arrays of small gimbaled mirrors to steer light arriving from one input (such as an optical fiber) to one output (such as another optical fiber) in an analog-steering manner. One commercially available system utilizing a 3D MEMS design, for example, specifies a port count of 320×320, typical insertion loss of 2.0 dB, and switching time of 25 ms (see S320 data sheet available at http://www.calient.net/products/s-series-photonic-switch/). The majority of the time required for switching in such 3D-MEMS device is generally consumed by the operation of a feedback loop required for precise angular mirror localization of the MEMS device.
Devices commonly defined and referred to in related art as “digital micro-mirror devices” or DMDs, have operational nature similar to that of MEMS devices, but are accepted as digital (as compared to analog) devices. In comparison with a MEMS device (an individual reflector or mirror of which can assume any orientation allowed by the structure of the corresponding gimbal or hinge), an individual reflector of a DMD device assumes only one of the two stable operational positions. As a result—and notwithstanding the superior switching speed of the DMD device over that of the MEMS device (50 microsecond or less vs. about 1 ms, respectively), lower consumption of electrical power, and longer time-to-failure (due to smaller dimensions and lower weights of individual mirrors)—where a MEMS-based device is operationally capable of implementing a 1-to-N (or 1×N) optical switch, the DMD can only redirect the incident beam of light to two pre-determined positions (1-to-2, or 1×2 optical switch). This structurally-limited operational restriction dramatically complicates a DMD-based architecture that has to be realized to implement an even 1×N switch with the use of currently-available DMDs. Indeed, instead of having the DMD reflectors/mirrors on one single platform, these mirrors have to be spatially separated and extremely precisely positioned such that light reflected by one individual mirror on the first platform can be then redirected by a second individual mirror of the second platform and so on. Although practically possible, such arborescent structure is simply not economically or practically feasible considering the existing method of manufacture of the DMDs. Moreover, as would be readily appreciated by a skilled artisan, failure of an individual mirror detrimentally impacts the performance of either a MEMS-based optical switch or a DMD-based optical switch.
The use of a liquid crystal display (LCD) spatial light modulators (SLMs) is another venue available for light-path modulation. It employs the (re)orientation of high aspect-ratio molecules in response to an applied voltage to impart birefringence and rotate a vector of polarization of incident light. In conjunction with a series of linear polarizers, this SLM functions as an addressable switch, which either passes or blocks light beam(s) incident on subsections of the SLM. A 6×6 multimode ribbon fiber design has recently been described by (H. Chou et al., J. Lightwave Technol., v. 30, pp. 1719-1725, 2012), which uses a custom molecule based phase SLM exhibiting 1 μs switching time but having a loss level of 20.5 dB, the 11.5 dB portion of which is inherent to the fan-out and polarizer/SLM design. Since this system uses light polarization as the switching mechanism, the light throughput is also extremely sensitive to variations in signal polarization, which is undesirable for many applications.
Therefore, the operational impediments of the existing technologies beg a question of how to implement an optical switch with the switching capabilities satisfying the N×M standard that requires no manual manipulation and exhibits switching speeds on the order of 10 microseconds and negligible performance impact due to mirror failure.